1. Field of the Invention
This invention relates to an apparatus for determining the fatigue limit of elastic materials, under completely reversed stress, in particular rubber, by applying a load which alternates between zero and a maximum value, and determining the number of load cycles which lead to the material breaking.
2. Description of the Prior Art
In order to test plastics and rubber for their dynamic loading capacity, these materials are subjected to continuous vibrations in order to determine the stresses or strains which exceed the fatigue limit under completely reversed stress and which lead to the material breaking after a certain number of alternating stresses. In this test, several identical samples are generally subjected in succession to graduated vibratory stresses and the relevent numbers of stress cycles endured are established (see "Lexikon der Kautschuk-Technik" by Jochen Schnetger, 1981, page 327). However, since it is impossible to determine an infinite fatigue limit, stresses where 10.sup.6 alternations of load in the vibration test are endured are usually stated as the fatigue limit under completely reversed stress in the alternating area and are represented graphically as so-called stress-cycle diagrams.
According thereto, it is known to subject individual samples of precisely prescribed dimensions to continuous vibrations of this type in suitable test machines. If, in so doing, these vibrations are applied at a frequency of 2 Hz in a device which is available on the market, then during the course of a test without a break, a period of time of about 1 week is required for the necessary endurance of 10.sup.6. However, since the tests have to be carried out for several strains, it is necessary to use more than one device, or a very long period of time is required, until all the desired results are obtained.
These long delays are, however, hardly beneficial and are often unjustifiable in many cases, for example during quality control or during the release of new mixtures.